Surfaces patterned with micro-scale fibers are attracting enormous attention for their unique features, including self-cleaning, anti-biofouling, and superhydrophobicity. Materials based on the arrays of flexible synthetic pillars immersed in soft gels exhibit homeostatic self-regulating properties and adaptivity. Most of these patterned surfaces are engineered by top-down methods, e.g. soft lithography. A large number of diverse patterning techniques, which use organic and polymeric materials, including solvent-assisted micro-molding, micro-contact printing, and dip-pen nanolithography, form the basis of contemporary soft lithography.
Design of the non-trivial 3D structures via bottom-up methods such as self-assembly and surface instabilities are highly desirable but technically challenging. For instance, electrohydrodynamic instability may yield 3D patterns at the interface between liquid dielectric materials without a pre-patterned mask. However, the progress is impeded by low controllability and irreproducibility of the emerging structures. External electric/magnetic fields are often used to promote colloidal self-assembly or form colloidal chains in electro- and magneto-rheological fluids along the direction of an applied field. Nontrivial structures can be generated in suspensions of metallo-dielectric patchy and dumbbell particles in external alternating electric or magnetic fields. However, these structures tend to disassemble as soon as the field is turned off unless fixed by crosslinkers. Recently developed methods of thermal annealing of colloidal patterns allow fixing some of the field-generated assemblies of spherical particles. Another promising alternative to the lithographic methods is a dynamic self-assembly occurring in out-of-equilibrium conditions. For example, dynamic self-assembly allows formation of diverse functional structures from suspensions of colloidal particles. The structures, which generally do not exist under equilibrium conditions, include radial magnetic asters, dynamic swimmers, self-healing membranes particle foams, self-assembled microtubes, and binary linear clusters.